This invention relates to drive unit assembly for a vehicle having a drive axle with a gear reduction assembly.
Gear reduction assemblies are used in many different types of vehicles to provide a desired drive torque and speed output at a vehicle wheel. Heavy-duty off-road vehicles such as lift trucks, container handles, rough terrain cranes, front end loaders, mining trucks, log haulers, etc., often require significant reductions in order to achieve high output torque at the wheel for adverse ground conditions. Other vehicles such as commercial on-highway hauling trucks, garbage trucks, buses, etc. that have the capability of hauling heavy loads also often require a gear reduction assembly to achieve a desired wheel output torque.
One type of reduction gear assembly is a planetary gear reduction assembly, which includes an internally toothed ring gear, a sun gear that is centrally positioned within the ring gear, and a plurality of planet gears in meshing engagement with both the sun and ring gears. The planet gears are mounted on a common planetary spider carrier that turns about the centerline defined by the sun gear. A reduction occurs because the sun gear has a fewer number of gear teeth than the ring gear. This planetary gear reduction assembly provides high power density in a very compact package and does not require support bearings for the input and output components. However, one disadvantage with this gear configuration is the input and output components are required to be concentric, thus this configuration cannot be used in applications that have inputs and outputs on different centerlines.
One type of reduction gear assembly for a non-concentric input/output configuration utilizes an input drive gear in meshing engagement with an output drive gear. Typically, the gears used in this configuration are required to be large in size because there is only one tooth set in contact. Further, the gears are rigidly mounted between bearings, which further increases the packaging area needed for the gear reduction components.
Another type of reduction gear assembly for a non-concentric input/output configuration utilizes a helical gear assembly with idler gears to carry higher loads for smaller gears. This gear configuration is used in axles for mass transit vehicle applications. Mass transit vehicles, such as trolley cars, buses, and the like, typically have seats aligned at the lateral sides of the vehicle, with a central aisle and floor extending along the vehicle. In order to facilitate entering and exiting from the vehicle, it is desirable to have the vehicle floor and aisle positioned relatively low to the ground. This provides faster cycle time during stops and facilitates boarding for all passengers, especially for elderly and disabled passengers, as well as for children.
Many such mass transit vehicles provide a rigid axle having an input positioned off-center near one wheel end to form an inverted portal axle configuration. The input is coupled to a driveshaft, which is powered by a vehicle engine and transmission. Due to the low floor configuration, the input to the axle is below the driving axis of rotation for the wheel ends. The helical gear assembly is used to transfer driving torque from the lower input position to the higher output position, as well as providing a desired gear reduction.
Traditionally, the helical gear assembly includes a helical pinion gear that is operatively coupled to a ring and pinion gear at the axle input and a helical driven gear that drives the associated wheel hub. A pair of idler gears is in meshing engagement with both the helical pinion and driven gears. This configuration, utilizing two (2) idler gears, can carry higher loads because there are two (2) tooth set contacts. However, this configuration is limited to close centerline mountings because the helical pinion gear and both idler gears are on the same centerline.
Accordingly, it is desirable to provide a gear reduction assembly that utilizes the high power density and packaging benefits of a planetary gear reduction but which can be incorporated into an axle with non-concentric input and output components. Further, it is desirable to package this improved gear reduction assembly into a portal axle configuration to provide an improved low floor profile to facilitate access to the vehicle as well as overcoming the other deficiencies in the art outlined above.
A drive axle includes a reduction gear assembly at each wheel end to drive vehicle wheels. The reduction gear assembly receives an input load from a vehicle driveline and transfers the load to an output at the vehicle wheel. The input and output to the gear reduction assembly are non-concentric. The gear reduction assembly includes an internally toothed ring gear that is rotatably supported within a gear housing. A drive gear, operatively coupled to the input, is in meshing engagement with the ring gear. A driven gear, operatively coupled to the output, is also in meshing engagement with the ring gear. The ring gear, drive gear, and driven gear are non-concentric. An idler gear assembly is interposed between the drive and driven gear to transfer load from the drive gear to the driven gear. The driven gear is larger than the drive gear to provide the desired gear reduction. The drive and driven gears run on the pitch line of the ring and idler gears such that the load is equally distributed amongst the gears, eliminating the need for support bearings for the drive and driven gears.
In the preferred embodiment, the idler gear assembly includes a pair of idler gears that are in meshing engagement with both the drive and driven gears. The drive gear defines a drive gear centerline and the idler gears define a common idler gear centerline that is spaced apart from and parallel to the drive gear centerline. The driven gear defines a driven gear centerline that is spaced apart from and parallel to the idler and drive gear centerlines.
The subject invention provides a gear reduction configuration that allows the distance between the drive and driven gear centerlines to be increased over traditional configurations because the drive gear centerline is below the idler gear centerline. Further, this configuration is one-third the size of traditional gear sets because three tooth sets are in contact. The subject invention provides smaller more compact gear reductions resulting in an improved low floor profile to facilitate access to a vehicle while still providing sufficient driving torque to the wheels. These and other features of the present invention can be best understood from the following specifications and drawings, the following of which is a brief description.